First Time Lo Filter Tune Up - NORCAL NC2030 Manual

C57 - 120 pf
C64 - 0.1uF
L6 L7 - 15T #26 T37-6; 10" of #26 enamel wire
30m only parts:
C53 - 7.5 pf
C57 C59 - 180 pf
L6 L7 - 19T #26 T37-6; 11" of #26 enamel wire
Install for both bands:
These caps must have the right orientation or it
C58 C60 - 50 pf trimmer cap.
will affect tune up (hot end, ground end). See the figures above!
Note: Make sure to wax the cores L6 and L7 as they tend to be microphonic. I used a birthday candle to
drip wax on the top and the bottom of the core to secure it from vibration. Alternative, I have also used
a craft glue gun and low temperature glue. This is a bit messy, but can be smoothed up a bit by using a
hair dryer set on "high" to melt the glue slightly. Make sure to secure the base of the coil to the board
and the windings around the core. Off hand, I think the wax method is more messy, but perhaps more
effective.
The entire point of the exercise is to damp vibrations in these two coils in order to kill microphonics.
These coils are the only two components on the entire radio that needs this special treatment.

First time LO filter tune up

Here we will tune up the LO filter for what ever frequency the PTO and the VXO mix to. At this point
in time, the PTO coil has not been properly tuned, so the mixed LO frequency is probably off by may be
100 to 150 KHz. In order to properly tune the PTO, the filter must first pass the mixed frequency so that
we can measure where we are with the on board AFA. From there we can start shifting the PTO
frequency to where it needs to be, which will require retuning the LO filter a couple of times also.
The LO filter section is composed of two tuned circuits, one tuned by C58 and the other tuned by C60.
The goal is to peak both variable capacitors to get between 1 and 1.5v at test point 3 (TP3). The voltage
is measured at TP3 using a normal voltmeter on a low voltage range such as a 2 or 3v scale. Although
variable capacitors C58 and C60 can be turned over a 360 degree range, the actual tuning range is done
over a 180 range. Turning these capacitors over a 360 degree range simply makes the variable
capacitors pass through their tuning range twice.
th
What will be done here is to move C58 a fraction of a turn (roughly 1/10 ), then sweep C60 through its
tuning ranging looking for a peak, then go back to C58 and turn another fraction and try again. Once a
peak is found, adjust both C58 and C60 for the best peak. C60 is the more critical setting of the two
caps, so be sure to do tuning sweeps with C60 and incremental changes in C58.
When the filter is tuned up, the peak TP3 ideally will be in the 1 to 1.5v range. We will not worry about
this at this time, but there are gain adjustment resistors that can get added in either the mixer or the LO
amp section or both to bring the detected voltage up to the needed range if it is low.
Norcal NC2030 v5 12-18-05
Page 69 of 128